With a day to go before the world learns exactly what Lance Armstrong said to Oprah Winfrey about his involvement in doping as a professional cyclist, the cancer charity he founded urged the fallen star to come clean.

"We expect Lance to be completely truthful and forthcoming in his interview and with all of us in the cancer community," Livestrong said in a statement released Wednesday. "We expect we will have more to say at that time."

The U.S. Anti-Doping Agency accused Armstrong in October of involvement in a sophisticated doping program while he was a professional cyclist. The world governing body for cycling, the International Cycling Union, stripped Armstrong of his seven Tour de France titles following the report. He's also been banned from the sport for life.

Winfrey's 2½-hour interview with Armstrong is to be aired Thursday and Friday on Winfrey's OWN cable network and on the Internet.

Photos: Lance Armstrong's rise and fall 28 photos

Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – After denying the allegations for years, cyclist Lance Armstrong admitted to using performance-enhancing drugs. As a result, he was stripped of his seven Tour de France titles and an Olympic bronze medal. Click through the gallery for a look at his life and career.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong, 17, competes in the Jeep Triathlon Grand Prix in 1988. He became a professional triathlete at age 16 and joined the U.S. National Cycling Team two years later.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong wins the 18th stage of the Tour de France in 1995. He finished the race for the first time that year, ending in 36th place.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong rides at the Ikon Ride for the Roses to benefit the Lance Armstrong Foundation in May 1998. He established the foundation to benefit cancer research after he was diagnosed with testicular cancer in 1996. After treatment, he was declared cancer-free in February 1997.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong leads his teammates during the final stage of the 1999 Tour de France.

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Lance Armstrong's rise and fall – Armstrong takes his honor lap on the Champs-Élysées in Paris after winning the Tour de France for the first time in 1999.

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Lance Armstrong's rise and fall – After winning the 2000 Tour de France, Armstrong holds his son Luke on his shoulders.

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Lance Armstrong's rise and fall – Armstrong rides during the 18th stage of the 2001 Tour de France. He won the tour that year for the third consecutive time.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong celebrates winning the 10th stage of the Tour de France in 2001.

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Lance Armstrong's rise and fall – After winning the 2001 Tour de France, Armstrong presents President George W. Bush with a U.S. Postal Service yellow jersey and a replica of the bike he used to win the race.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong celebrates on the podium after winning the Tour de France by 61 seconds in 2003.

Lance Armstrong's rise and fall – After his sixth consecutive Tour de France win, Armstrong attends a celebration in his honor in front of the Texas State Capitol in Austin.

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Lance Armstrong's rise and fall – Armstrong arrives at the 2005 American Music Awards in Los Angeles with then-fiancee Sheryl Crow. The couple never made it down the aisle, splitting up the following year.

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Lance Armstrong's rise and fall – Armstrong holds up a paper displaying the number seven at the start of the Tour de France in 2005. He went on to win his seventh consecutive Tour de France.

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Lance Armstrong's rise and fall – Armstrong testifies during a Senate hearing in 2008 on Capitol Hill. The hearing focused on finding a cure for cancer in the 21st century.

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Lance Armstrong's rise and fall – In 2009, Armstrong suffered a broken collarbone after falling during a race in Spain.

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Lance Armstrong's rise and fall – Young Armstrong fans write messages on the ground ahead of the 2009 Tour de France. He came in third place that year.

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Lance Armstrong's rise and fall – Armstrong launches the three-day Livestrong Global Cancer Summit in 2009 in Dublin, Ireland. The event was organized by his foundation.

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Lance Armstrong's rise and fall – In May 2010, Armstrong crashes during the Amgen Tour of California. That same day, he denied allegations of doping made by former teammate Floyd Landis.

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Lance Armstrong's rise and fall – Armstrong looks back as he rides during the 2010 Tour de France.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong's son Luke; his twin daughters, Isabelle and Grace; and his 1-year-old son, Max, stand outside the Radio Shack team bus on a rest day during the 2010 Tour de France.

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Lance Armstrong's rise and fall – Armstrong finished 23rd in the 2010 Tour de France. He announced his retirement from the world of professional cycling in February 2011. He said he wanted to devote more time to his family and the fight against cancer.

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Lance Armstrong's rise and fall – The frame of Armstrong's bike is engraved with the names of his four children at the time and the Spanish word for five, "cinco." His fifth child, Olivia, was born in October 2010.

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Photos: Lance Armstrong's rise and fall28 photos

Lance Armstrong's rise and fall – Armstrong competes in the 70.3 Ironman Triathlon in Panama City, Florida, in February 2012. He went on to claim two Half Ironman triathlon titles by June of that year.

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Lance Armstrong's rise and fall – Armstrong addresses participants at the Livestrong Challenge Ride on October 21, 2012, days after he stepped down as chairman of his Livestrong cancer charity.

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Lance Armstrong's rise and fall – International Cycling Union President Pat McQuaid announces the decision to strip Armstrong of his seven Tour de France wins and ban him from the tournament for life on October 22, 2012. "Lance Armstrong has no place in cycling," he said.

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Lance Armstrong's rise and fall – In January 2013, Armstrong speaks with Oprah Winfrey about the controversy surrounding his cycling career. He admitted, unequivocally and for the first time, that he used performance-enhancing drugs while competing.

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If true, such an admission would be a stunning reversal after years of vigorous denials, including lawsuits filed against accusers.

But it still will not be enough to reverse the lifetime ban and other sanctions that have kept him from participating in some triathlons -- the three-event sport he took up after retiring from cycling.

"Only when Mr. Armstrong makes a full confession under oath -- and tells the anti-doping authorities all he knows about doping activities -- can any legal and proper process for him to seek any reopening or reconsideration of his lifetime ban commence," said David Howman, director general of the World Anti-Doping Agency.

Winfrey said her team and Armstrong's camp had originally agreed not to leak details of the interview, and that she was surprised to find that not long after the interview, news reports were saying part of what Armstrong told her had "already been confirmed."

Winfrey declined to characterize Armstrong's answers or offer preview quotes, but said Armstrong came ready.

She said the former cyclist was forthcoming in what she described as an exhausting and intense interview taped Monday in Armstrong's hometown of Austin, Texas.

"We were mesmerized and riveted by some of his answers," she told CBS.

While the interview was revealing, Winfrey said, his demeanor surprised her. "He did not come clean in the manner that I expected," she said without elaborating.

Asked whether she thought it was difficult for him to "come clean" to her, Winfrey responded, "Yes. I think the entire interview was difficult."

It was not immediately clear why Armstrong apparently chose to acknowledge doping after years of denials.

Juliet Macur, the New York Times reporter who broke the news on January 4 that Armstrong was considering an admission of doping, said the athlete is too driven to accept life without sports.

"He has had (several months) to think about how he is lonely, how he doesn't have the adulation of fans at the finish line and nobody to beat right now," she said. "And it's driving him nuts."

Armstrong has been seeking to participate in triathlons sanctioned by U.S. Olympic authorities. Armstrong excelled at triathlons as a teenager and went back to the sport after retiring from cycling. He has been banned from officially sanctioned events.

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Paul Willerton, who raced with Armstrong in the early 1990s, said any confession would be "just a starting point" for the cycling star.

"There are a lot of people still lying," Willerton said, naming former Armstrong consultant Dr. Michele Ferrari, and Johan Bruyneel, the onetime director of Armstrong's U.S. Postal Service team. "These guys are still perpetrating the lies and deception that Lance ruled over, and Lance holds the keys. He wants his control back, and he desperately wants to be liked by the American public. And you can't have it all."

The USADA suspended Ferrari for life in July, naming him as part of a large-scale doping conspiracy. Bruyneel is battling similar charges by the agency and said in October that he was "stunned" that its findings on Armstrong revealed details of the allegations against him.

Livestrong is also a consideration.

In October, Armstrong resigned as chairman of the charity he founded "to spare the foundation any negative effects as a result of controversy surrounding my cycling career," according to a statement posted to the group's website at the time. A few weeks later, he left the board entirely amid concerns that his involvement was harming the charity.

On Monday, he visited the charity and "expressed his regret for the stress the team suffered in recent years as a result of the controversy surrounding his cycling career," the organization said in a statement.

"Inspired by the people with cancer whom we serve, we feel confident and optimistic about the Foundation's future and welcome an end to speculation," the group said.

Meanwhile, the cycling world is eagerly -- and in some cases, perhaps, anxiously -- awaiting to hear what Armstrong has to say.

As the World Anti-Doping Agency noted, Armstrong could begin to redeem himself by speaking out about others in cycling with deep involvement in doping.

That's what former cyclist John Eustice expects when Armstrong speaks.

"I think what he'll do is explain how it all works," he said.

Willerton agreed, saying it's one last way for Armstrong to control the narrative swirling around him.

"He's cornered in the sense that he wants to maintain control and he knows that he holds the keys to the people around him who were complicit in what he did," Willerton said. "And that's really the most valuable thing he has to offer at this point."

However, on Tuesday, a source familiar with the matter denied to CNN a report in The New York Times that Armstrong was planning to testify against several powerful people in cycling who have facilitated doping.

SCA Promotions paid Armstrong millions for his Tour de France wins, and now wants its money back. Armstrong sued the company after it raised questions about allegations involving him, and testified under oath that he'd never doped, attorney Jeff Tillotson said Wednesday.

"No matter what he says tomorrow night, based on the evidence we have, we have a compelling legal case for the return of the money we paid him," he said. "But we're specifically looking to see which of the doping allegations that we raised and developed in our case he's going to acknowledge as true."

Meanwhile, the federal government is evaluating whether it will intervene in a whistle-blower lawsuit filed by a former Armstrong teammate. The lawsuit accuses managers for the team they both raced for of defrauding the federal government of millions of dollars because they knew about the drug use and didn't do anything.

A source familiar with the matter confirmed to CNN that lawyers for Armstrong are in discussions with the Justice Department regarding the case. The government has until Thursday to intervene, not intervene or ask for an extension, the source said.

The Justice Department declined Tuesday to comment on potential civil action against Armstrong, saying the whistle-blower suit is under court seal.

A spokesman for the U.S. Postal Service told CNN it could not discuss any of the legal issues associated with Armstrong and their prior relationship.